As far as I know the technical details, I have been explained by a developer that this is a complicated matter which is very hard to solve. The allocation of RAM always happens through the OS. When I VST instrument is loaded, it is the VST instrument that is “asking RAM” through Nuendo, to the OS. When the VST instrument is unloaded it “releases” the used RAM. Since the VST instrument has asked for RAM through Nuendo, this RAM however is still “held” by Nuendo. Nuendo does want to release that RAM, but can’t because the OS won’t take orders from Nuendo. (Remember it was the VST intrument that has asked the RAM, although through Nuendo)
I have understood that there are scenario’s to avoid that, but since every DAW is loading plugins & instruments in a different way, it is pretty much impossible to create a solutution for each and every DAW.
I might have made a few mistakes here, but this is as I recall it from a long talk with one of our developers.